1. Field Of The Invention
The invention is a catalytic process for converting crude petroleum fractions to gasoline. More particularly the invention is a process for converting petroleum fractions by both fluid catalytic cracking (FCC) and catalytic reforming.
2. Description Of Related Methods In The Field
In the fluid catalytic cracking (FCC) process a petroleum derived hydrocarbon charge stock is contacted with hot regenerated catalyst in a reaction zone. The charge stock is converted by cracking to lower boiling hydrocarbons and coke. The lower boiling hydrocarbon vapor and spent catalyst are separated in a containment vessel, termed in the art the reactor vessel. Separated spent catalyst is steam stripped of entrained vapor and the remaining spent catalyst coated with a layer of unstrippable coke is passed from the reactor vessel to a catalyst regenerator vessel. There, spent catalyst is regenerated by controlled oxidation of the coke coating to carbon dioxide and carbon monoxide. An active regenerated catalyst, substantially free of coke is thereby produced.
Separated lower boiling hydrocarbon vapor, stripped vapor and spent stripping steam is withdrawn from the reactor vessel and passed to a fractionation train where cracked hydrocarbon vapors are separated by fractional distillation into the desired intermediate fractions. Any number of intermediate fractions can be made based on refinery configuration and product demand. For example, product fractions may include a gaseous fraction, naphtha, kerosene, diesel oil, gas oil and vacuum gas oil. Of these fractions, the naphtha fraction is the most desirable because of its use as an automobile fuel blending stock after further processing. The intermediate fractions comprising naphtha, kerosene and diesel oil may be used for their fuel value. In the alternative they may be processed to produce additional naphtha suitable for blending into gasoline. The heavy fractions comprising gas oil and vacuum gas oil may be used for the production of heavy fuel oil. A portion of the heavy fraction may optionally be recycled to the fluid catalytic cracking reaction zone to produce additional lower boiling hydrocarbons, including an additional increment of gasoline.
U.S. Pat. No. 4,422,925 to D. Williams et al. teaches a process for the fluid catalytic cracking (FCC) of a plurality of hydrocarbon feedstocks. In the process a gaseous paraffinic hydrocarbon is used as a lift gas to fluidize a cracking catalyst in a riser (transfer line) reactor. Naphtha and gas oil feedstocks are cracked to yield liquid fuels.
Catalytic reforming is a process for converting crude petroleum fractions to high octane naphtha suitable for blending in gasoline. Feedstocks for the catalytic reforming process are typically straight run naphthas from crude petroleum which have been subjected to hydrodesulfurization. Catalytic reforming reactions include dehydrogenation, isomerization and hydrocracking. The dehydrogenation reactions typically include the dehydroisomerization of alkylcyclopentanes to aromatics, the dehydrogenation of paraffins to olefins, the dehydrogenation of cyclohexanes to aromatics, and the dehydrocyclization of paraffins and olefins to aromatics. The conversion of cyclic paraffins and n-paraffins to aromatics is most important because of the high octane of the resulting aromatic product compared to the low octane of the n-paraffin feedstock. The isomerization reactions include isomerization of n-paraffins to isoparaffins, the hydroisomerization of olefins to isoparaffins, and the isomerization of substituted aromatics. Hydrogenation reactions include the hydrocracking of paraffins and hydrodesulfurization of residual sulfur compounds remaining in the feedstock.